1. Field of the Invention
This invention relates to a synergistic combination of two insecticides, boron-containing compounds and synthetic pyrethroids, which when used in combination, give a synergistic result in providing improved resistance to insect attack on wood treated with this combination. Wood treated with this combination, and a method of treating wood, is also included in the present invention.
2. Description of the Prior Art
Wood and wood-based materials, including cellulosic composites and plastic-wood composites, are susceptible to damage from insect pests including ants, beetles and termites.
A particular species of termite, the Formosan subterranean termite, Coptotermes formosanus Shiraki, is of particular concern. This termite species is the most widely distributed and damaging termite pest in tropical and subtropical regions of the world and is responsible for tens of millions of dollars each year in costs of damages and control in the State of Hawaii alone. The Formosan termite is an increasingly serious problem across the southern United States as well. The rapid feeding rate, large colony size and aggressive foraging of this termite species make it especially challenging with respect to developing wood treatment substances designed to protect wood and wood products from attack by this particular pest. It is desirable, therefore, to develop treatments which are capable of protecting wood against such an aggressive organism.
Currently, a variety of insecticides, including creosote, chrome-copper-arsenate, organophosphates and boron compounds, are available to protect wood and wood composites against insect attack. Synthetic pyrethroids are also used to protect against pests but are not as economical to use in the amounts needed for sufficient pest control.
U.S. Pat. Nos. 5,480,638 and 5,575,996 disclose a powdered insecticide bait composition comprised of pet food, powdered pyrethrin and boric acid. This patent does not disclose the use of pyrethroids in combination with boron compounds as a wood treatment composition.
U.S. Pat. No. 5,516,620 relates to a controlled release composition in which a insecticide is encapsulated in a starch-borax-urea matrix. This patent does not disclose boron compounds as insecticides or for use in wood treatment products.
U.S. Pat. No. 5,880,142 discloses a composition suitable for controlling termites comprised of a compound of a specific chemical formula used in combination with a pyrethroid. Boron is not disclosed for use as an insecticide.
U.S. Pat. No. 5,916,356 discloses a wood preservative composition comprising a synergistic combination of a biocidal metal compound and a fungicidal compound having a triazole group. The biocidal metal compound can be zinc in the form of an inorganic salt such as zinc borate. This patent does not disclose boron compounds in combination with pyrethroids.
It is desired, therefore, to develop a wood treatment substance capable of protecting wood against extremely aggressive termite attack in an economical manner.
The present invention fulfills the above need by providing an unusually effective and economical wood treatment that protects wood and wood products against such aggressive termite attack. The present invention provides a unique combination of two classes of insecticides, specifically boron-containing insecticides and synthetic pyrethroids, which in combination provide a more complete resistance to insect attack in a more economical manner, than either compound used alone. A method of treating wood, in particular composite wood materials, with the synergistic combination is included in the present invention, as is the wood treated by this combination.
It is an object of the invention therefore, to provide a combination of insecticides to resist insect attack in wood treated with such substances, in an economical manner.
It is an additional object of the present invention to provide a wood treatment that can protect wood against the extremely aggressive Formosan termite.
It is a further object of the present invention to provide a wood treatment which can resist Formosan termite attack using boron-containing insecticides in combination with synthetic pyrethroids.
These and other objects of the invention will become apparent from the following description and appended claims.
Accordingly, the present invention provides a wood treatment material comprising a synergistic combination of a boron-containing insecticide and a synthetic pyrethroid. As used herein, the term xe2x80x9cwood treatment materialxe2x80x9d refers to this synergistic combination of insecticides, which may be used with other additives such as resins or solvents, and which is applied to wood by a variety of methods including, but not limited to, spraying, dipping, pressure treating, addition during formation of engineered wood, and other methods known to those skilled in the art that are used to apply such substances to wood.
As used herein, the term xe2x80x9cboron-containing insecticidexe2x80x9d includes insecticides containing at least one boron compound selected from the group including boron, alkali metal salts of boron, alkaline earth metal salts of boron, metal salts of boron, oxides of boron, boric acid, boric acid esters and salts of these.
It is thought that in respect to the metal salts of boron, that the active part of the compound is the boron, rather than metallic, portion. Preferred boron compounds are the alkali metal, alkaline earth metal or other metal salts of boron. Most preferred is zinc borate.
As used herein, the term xe2x80x9csynthetic pyrethroidxe2x80x9d includes a group of insect growth regulators that act as neurotoxins and are especially effective against insects that are destructive in the adult stage. This class of insecticides is desirable for pest control because it is considered to be of low toxicity to animals and humans. However, it is preferred to use pyrethroids in combination with other insecticides due to their high cost. Suitable synthetic pyrethroids include deltamethrin, cyfluthrin, permethrin, trilomethrin, cypermethrin, resmethrin and other synthetic pyrethroids. A preferred synthetic pyrethroid is deltamethrin.
As used herein, the term xe2x80x9cwoodxe2x80x9d includes a variety of wood and wood-based materials, including but not limited to logs and other types of dried lumber, green lumber, fiberboards, strand board, laminated veneer lumber, cellulosic composites, plastic wood composites and other types of wood, wood composites and engineered wood formed from wood chips, strands, veneers and adhesives.
On a weight to weight percent basis, the boron-containing compound will be present in the final wood product in an amount of about 0.05 wt. % to about 2.0 wt. %, more preferably about 0.20 wt. % to about 1.0 wt. %. The synthetic pyrethroid will be present in the final wood product in an amount of between about 1 ppm to about 1000 ppm, more preferably between about 5 ppm and about 100 ppm. All weight percent or part-per-million values are based on the total weight of the wood product after treatment.
The insecticides can be applied on the surface of the wood, as in spraying or dipping the wood in a solution containing both insecticides. Other constituents of the solution include a paraffin wax emulsion and water. The insecticides can also be applied to the wood with pressure treatment that is commonly used on solid or engineered wood. A third method, particularly for engineered wood, is to treat the wood chips or strands with the insecticide combination in powder or liquid form prior to formation of the composite wood boards. Wood may be treated by more than one of these methods.
In the third method, the insecticides are combined with wood flakes, chips or strands, a phenolic resin and a water repellant, and fabricated into a wood composite board. This last step may be accomplished in a heated high-pressure press. These severe processing conditions often result in reduced performance of additives such as insecticides. Unexpectedly, the performance of a boron compound in combination with a pyrethroid was not reduced, but was actually improved.
This combination of insecticides has proven to be unusually effective in providing resistance to attack by Formosan termites. It is also expected that the combination will be effective against a variety of other less aggressive pests, including ants, beetles, wasps and other insects.